1. Field of the Invention
The present invention relates in general to mass spectrometers for analyzing differences in the mass of atomic or molecular ions by utilizing electromagnetic interactions, and relates in particular to a high frequency type mass spectrometer which performs mass separation of the ions with the use of high frequency electrical field.
2. Description of the Related Art
FIG. 11 shows a conventional mass spectrometer of the high frequency separation type called Topatron. This type of mass spectrometer comprises: an ion source 21 for releasing sample ions; an energy filter 22 for passing only selected ions having a specific energy level; a current detection electrode 23; an analyzer section 25 comprising a plurality of electrodes 24; an extractor electrode 27 for pulling out ions; a repeller electrode 26 for passing only those ions having the highest energy level and repelling those ions having an energy less than the specified level; a collector electrode 28 for collecting the ions that passed through the electrode group; and an ammeter 29 provided for the collector electrode 28.
The sample ions released from the ion source 21 are guided to the energy filter 22 so as to pass only those ions having a specific energy level, and the total energy of the ions having the maximum energy level is determined by measuring the ion current with the current detection electrode 23. A high frequency electrical field is applied to the plurality of electrodes 24 in the analyzer section 25 so that only those ions (having the specific energy level) that are in resonance with the applied high frequency field are allowed to pass through, and the energy of all other ions are diminished. The repeller electrode 26 selectively passes only those ions having the highest energy level, and after collecting the ions with the collector electrode 28, the amount of the collected ions is determined from the reading of the ammeter 29. By comparing the ratio of the current measured with the current detection electrode 23 to that measured with the ammeter, it is possible to compute the ratio (of the energies) of the target ions to the injected sample ions.
In this type of apparatus, it is necessary to provide a large number of electrodes 24 to improve the resolving power. The flight distance (mean free path) in such an arrangement of the electrodes is inevitably increased, and the apparatus does not function unless a high vacuum (higher than 10.sup.-5 torr) is provided. Furthermore, this type of apparatus has other problems such as the large size of the equipment because of the requirement of a large number of electrodes.